Abscisic acid (S-abscisic acid, S-ABA, ABA) is a naturally occurring plant hormone found in all higher plants (Cutler and Krochko. 1999. Trends in Plant Science. 4: 472-478. Finkelstein and Rock. 2002. The Arabidopsis Book. ASPB, Monona, Md., 1-52). S-ABA is involved in many major processes during plant growth and development including dormancy, germination, bud break, flowering, fruit set, general growth and development, stress tolerance, ripening, maturation, organ abscission and senescence. S-ABA also plays an important role in plant tolerance to environmental stresses, such as drought, cold, and excessive salinity.
One key role of S-ABA in regulating physiological responses of plants is to act as a signal of reduced water availability to reduce water loss, inhibit growth and induce adaptive responses. All these functions are related to stomatal closure of plant leaves (Raschke and Hedrich, 1985, Planta, 163: 105-118). When stomata close, plants conserve water to survive in environmental stresses. However, stomatal closure also results in the reduction of photosynthesis, and respiration and thus growth. Stomatal closure is a rapid response of plants to S-ABA. The mechanism of S-ABA that causes stomatal closure has been studied, and the effect has been shown to be due primarily to S-ABA's effect on guard cell ion channels. Specifically, S-ABA blocks H+ extrusion and K+ influx from guard cells and promotes K+, Cl−, and malate extrusion and Ca2+ influx. The net effect of S-ABA is to reduce the total osmotica in the guard cells, which in turn decreases the water content in the cell. This causes the guard cells to lose their turgor and thus close the stomata (Assmann 2004 In: Plant Hormones Biosynthesis, Signal Transduction, Action! ed. Davies, p 391-412). The closing of stomata results in reduced transpiration of the plant leaf. In grapes, application of S-ABA has been reported to increase stomatal resistance in grapevines, thereby reducing the gas exchange and stomatal transpiration of the leaves (During and Broquedis, 1980, Sci. Hort., 13: 253-260).
The exogenous application of S-ABA to red grapes prior to harvest has been shown to increase the accumulation of anthocyanins and increase the red color of the grape berry skins (e.g. Han, D. H, S. M. Lee, and S. B. Kim. 1996, J. Kor. Soc. Hort. Sci. 37: 416-420; Lee, K. S., J. C. Less, Y. S. Hwang, and I. B. Hur, 1997, J. Kor. Soc. Hort. Sci. 38: 717-721; Kondo, S., Masuda, E. and Inoue, K., 1998, Acta Hort., 464: 35-40; Pepe, M. C., Fidelibus, M. W., Dokoozlian, N. 2006, HortScience, 41:1440-1445).
The sensory characteristics of wine, such as aroma and flavor, are complex and there is interest in altering wine grape berry and/or wine characteristics to produce more diverse or better wine or wines with different balances of sensory characteristics. A patent application has been filed (Quaghebeur, K., 2005, US 2005/0198896 A1) claiming that ABA application enhances wine quality as a consequence of simulating drought in the grapevine leading to reduction in grape berry size in conjunction with increased sugar content. However, no mention is made of ABA application affecting sensory characteristics such as aroma, bouquet, flavor, mouthfeel, astringency, balance, complexity, and finish. The literature reports that the effect of S-ABA application on grapes is to increase berry and cluster weight (Han, D. H, S. M. Lee, and S. B. Kim. 1996. J. Kor. Soc. Hort. Sci. 37: 416-420). While the effect of S-ABA to increase red color of red grapes has been studied and reported, there are no previous reports on the effect of and the use of S-ABA on white grapes to affect the various sensory characteristics of white grapes and/or the resulting wine.